Thanks for the accurate info. That is the piston, however. I removed it from the master to get a size but you cant see the indent from the top view I guess.
And you are correct, it is a "used" master since Ive had it on the car for a week or so. The elongated holes I suppose would be for centering but it self centers. Any scuff marks are from me taking it on and off.
I got my pedal ratio based on: pedal top pivot to pedal / pedal top pivot to booster connection
Its the stock holes for the OEM 86 gm brake booster setup. Still think I should be looking for 6:1, its easy enough to make a new hole?